Bases or base precursors are frequently incorporated into heat developable light-sensitive materials for the purpose of accelerating development upon heating. In view of preservability of the light-sensitive materials, it is preferred to employ base precursors which release basic substances upon heat decomposition.
Examples of typical base precursors are described in British Pat. No. 998,949. A preferred base precursor is a salt of a carboxylic acid and an organic base, and examples of the suitable carboxylic acids include trichloroacetic acid and trifluoroacetic acid and examples of the suitable bases include guanidine, piperidine, morpholine, p-toluidine and 2-picoline, etc.
Guanidine trichloroacetate as described in U.S. Pat. No. 3,220,846 is particularly preferred. Further, aldonic amides as described in Japanese patent application (OPI) No. 22625/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") are preferably used because they decompose at a high temperature to form bases.
When these heretofore known base precursors are employed, however, the following problems are often encountered. Specifically, a relatively long time is required for obtaining images and a high level of fog is formed. Further, they have a disadvantage in that they are susceptive to air and humidity and decompose. As a result, the photographic properties of the light-sensitive materials containing them undergo a change and the preservability of the light-sensitive materials is seriously degraded.